Internal gear pump

ABSTRACT

An internal gear pump is a return feed pump for a hydraulic vehicle braking system. The internal gear pump includes a filling part formed by two flexible sheet metal parts connected by an axial sealing element that is vulcanized in place and, in side view, is U-shaped. The axial sealing element is configured to improve the efficiency of the internal gear pump and allows large production tolerances.

The invention relates to an internal gear pump, in particular for a hydraulic vehicle brake system having the features of the preamble of claim 1. Internal gear pumps of this kind are employed in slip-controlled and/or power-operated vehicle brake systems instead of conventional piston pumps and are often referred to as return pumps, although this is not entirely accurate.

PRIOR ART

Internal gear pumps are known. They have a pinion, i.e. an externally toothed gearwheel, which is arranged eccentrically in an internally toothed annulus and meshes with the annulus at one point on the circumference or in one section of the circumference.

Driving the pinion in rotation causes the annulus to be driven in rotation as well, and the internal gear pump delivers fluid in a manner known per se, the fluid delivered in a hydraulic vehicle brake system being brake fluid. The pinion and the annulus can also be referred to as gearwheels of the internal gear pump.

Opposite the section of the circumference in which the pinion meshes with the annulus, the internal gear pump has a crescent-shaped free space between the pinion and the annulus, in which a filler piece is arranged. The filler piece can normally be pivoted about an axis parallel to the axis of the internal gear pump. Owing to the curved shape, the filler piece is also referred to as a crescent, and internal gear pumps with a filler piece of this kind are also referred to as crescent pumps. Tooth tips of teeth of the pinion rest on a concavely rounded inner side of the filler piece, and tooth tips of the annulus rest on an outward-curved outer side of the filler piece. As the gear pump is driven, the tooth tips of the teeth of the pinion and of the annulus slide along the inner and outer side of the filler piece, respectively. The filler piece encloses interspaces between the teeth of the pinion and between the teeth of the annulus at the circumference, thus enclosing fluid volumes in the interspaces between the teeth of the pinion and of the annulus, said volumes being pumped from a pump inlet to a pump outlet by the rotary driving of the pinion and the annulus. The pump inlet forms a suction side and the pump outlet forms a pressure side of the internal gear pump.

Patent EP 1 760 315 A2 discloses an internal gear pump of this kind, the filler piece of which is divided in the circumferential direction and has an inner part, referred to as a segment carrier, and an outer part, referred to as a segment. Leaf springs arranged between the inner part and the outer part press the inner part and the outer part radially apart and against the tooth tips of the teeth of the pinion and of the annulus in order to ensure good contact with the tooth tips and hence a good sealing effect, which is a prerequisite for a high efficiency of the internal gear pump. When the internal gear pump builds up a pressure during operation, this pressure acts on a gap or interspace between the inner part and the outer part of the filler piece. The pressure buildup during operation of the internal gear pump presses the inner part and the outer part of the filler piece of the known internal gear pump apart and against the tooth tips of the teeth of the pinion and the annulus, supplementing the effect of the leaf springs, and thereby improves the sealing effect.

For axial compensation, the known internal gear pump has axial plates, which are arranged on both sides of the gearwheels and of the filler piece in a manner which prevents relative rotation and allows axial movement. On outer sides, which face away from the gearwheels and the filler piece, the axial plates are subjected to a fluid delivery pressure by a pressure side, i.e. an outlet, of the internal gear pump and, as a result, are pressed inward against the gearwheels and the filler piece of the internal gear pump in order to form a seal there.

The known internal gear pump has a large number of expensive components and it is complex to assemble. Given smaller dimensions for an internal gear pump of a hydraulic vehicle brake system, precision of the components, which is necessary for good volumetric efficiency, is scarcely achievable at an economically justifiable cost.

DISCLOSURE OF THE INVENTION

The filler piece of the internal gear pump according to the invention, having the features of claim 1, has an inner part and an outer part. Tooth tips of teeth of the pinion of the internal gear pump rest on an inner side of the inner part, and tooth tips of teeth of the annulus of the internal gear pump rest on an outer side of the outer part. An axial sealing element is arranged between the inner part and the outer part, said sealing element being composed, in particular, of an elastomer and sealing off sides of the filler piece, i.e. forming a seal between the filler piece and axial plates of the internal gear pump, if it has the axial plates. If there are no axial plates, the sealing element forms a seal with respect to inner end faces of a pump casing or of a pump space, against which the gearwheels and the filler piece of the internal gear pump rest. The invention improves sealing between a suction side and a pressure side, i.e. between an inlet and outlet of the internal gear pump, and thereby increases the efficiency thereof. Moreover, the invention allows larger production tolerances for the components of the internal gear pump and, inter alia, renders axial plates for axial compensation superfluous.

The dependent claims relate to advantageous embodiments and developments of the invention indicated in claim 1.

BRIEF DESCRIPTION OF THE DRAWING

The invention is explained in greater detail below by means of an embodiment illustrated in the drawing. The single FIGURE shows a side view of an internal gear pump according to the invention.

EMBODIMENT OF THE INVENTION

The internal gear pump 1 according to the invention, which is illustrated in the drawing, is provided as a hydraulic or “return” pump in a hydraulic vehicle brake system having traction control. It has a pinion 2, i.e. an externally toothed gearwheel, which is arranged in a manner fixed against relative rotation on a pump shaft 3. The pinion 2 is arranged eccentrically in an internally toothed annulus 4, which is mounted rotatably in a pump casing 5. Housing covers are not shown to ensure that the inner parts of the internal gear pump 1 can be seen. The pinion 2 meshes with the annulus 4 in one section of the circumference. Driving the pinion 2 in rotation by means of the pump shaft 3 drives the annulus 4 in rotation as well, with the result that the internal gear pump 1 delivers fluid in a manner known per se, the fluid being brake fluid in the illustrated embodiment of the internal gear pump 1 according to the invention. The pinion 2 and the annulus 4 are also referred to as gearwheels 2, 4 of the internal gear pump 1. Opposite the section of the circumference in which the gearwheels 2, 4 intermesh, the internal gear pump 1 has a crescent-shaped free space 6 between the pinion 2 and the annulus 4, which can also be referred to as the pump space. Bores parallel to the pump shaft 3 open into the free space 6 in the region of both ends of the free space 6. One of the two bores forms a pump inlet 7, and the other forms a pump outlet 8. The pump inlet 7 can also be taken to be the suction side and the pump outlet 8 can be taken to be the pressure side of the internal gear pump 1.

A filler piece 9 is arranged in the free space 6, between the pump inlet 7 and the pump outlet 8, often also being referred to as a crescent or crescent piece owing to its shape. The filler piece 9 separates a suction and inlet side of the free space 6 from a pressure and outlet side. The filler piece 9 has an outer part 10 and an inner part 11. The outer part 10 and the inner part 11 are in the form of circular arcs corresponding to tip circles of the gearwheels 2, 4. An outer side of the outer part 10 rests on tooth tips of teeth of the annulus 4, and an inner side of the inner part 11 rests on tooth tips of teeth of the pinion 2. The outer part 10 is angled radially inward at a suction-side end and forms a yoke 12 of the filler piece 9. It would also be possible, instead, for the inner part 11 to be angled radially outward at the suction-side end thereof. On the suction side, the filler piece 9 is supported by means of the yoke 12 thereof on a stop pin 13, which passes through the free space 6 on the suction side of the filler piece 9, parallel to the pump shaft 3. The outer part 10 and the inner part 11 are bent sheet metal parts and are produced by bending from sheet metal strips.

An axial sealing element 14, which is composed of an elastomer, is arranged between the outer part 10 and the inner part 11. The axial sealing element 14 is U-shaped in side view and has a relatively solid yoke region 15 and two legs 16, 17. The word “solid” is intended to indicate that the yoke region 15 extends a relatively long way from the yoke 12 of the filler piece 9 in the direction of the pressure side of the internal gear pump 1; in the illustrated embodiment of the invention, the extent of the yoke region 15 in the circumferential direction is approximately as great as a radial spacing of the tip circles of the gearwheels 2, 4 at the location of the yoke region 15 of the axial sealing element 14. The legs 16, 17 of the axial sealing element 14 extend integrally from the yoke region 15 along an inner side of the outer part 10 and the outer side of the inner part 11 of the filler piece 9, wherein the legs 16, 17 of the sealing element 14 are shorter in the circumferential direction than the outer part 10 and the inner part 11 of the filler piece 9. Between the legs 16, 17 of the sealing element 14 there is a cavity 18 which, like the filler piece 9, is open toward the pump outlet 8, i.e. toward the pressure side of the internal gear pump 1, and is subjected to a pressure of the brake fluid on the pressure side and in the pump outlet 8 of the internal gear pump 1.

The axial sealing element 14 is connected to the outer part 10 and to the inner part 11 of the filler piece 9, being adhesively bonded for example. In the illustrated embodiment, the sealing element 14 is vulcanized onto the outer part 16 and the inner part 17. For the production of the sealing element 14, the outer part 10 and the inner part 11 of the filler piece 9 can be inserted as shaping elements into an injection mold, for example, with the result that production of the sealing element 14 and connection to the outer part 10 and the inner part 11 take place in a single production step. The axial sealing element 14 can also be produced separately and then connected to the outer part 10 and the inner part 11 of the filler piece 9. The sealing element 14 connects the outer part 10 and the inner part 11 to one another. The solid yoke region 15 of the sealing element 14 presses the outer part 10 and the inner part 11 apart, i.e. presses the outer part 10 outward against the tooth tips of the teeth of the annulus 4 and the inner part 11 inward against the tooth tips of the teeth of the pinion 2. This ensures sealing between the filler piece 9 and the teeth of the gearwheels 2, 4 when the internal gear pump 1 is unpressurized. When the internal gear pump 1 is delivering, the pressure on the pressure side of the internal gear pump 1 pressurizes the cavity 18 between the legs 16, 17 of the sealing element 14 and presses the outer part 10 outward against the tooth tips of the teeth of the annulus 4 and the inner part 11 inward against the tooth tips of the teeth of the pinion 2, thereby ensuring sealing, even when the delivery pressure is high.

The axial sealing element 14 exerts a lateral sealing action. Subjecting the cavity 18 between the legs 16, 17 of the sealing element 14 to the pressure of the pressure side of the internal gear pump 1 exerts a radial pressure on the legs 16, 17, thereby pressing the legs 16, 17 laterally outward, improving the lateral sealing action of the axial sealing element 14 as the delivery pressure of the internal gear pump 1 rises. The axial sealing element 14 ensures a good sealing effect, both when the internal gear pump 1 is unpressurized and during operation.

The internal gear pump 1 has axial plates 19 on both sides, said plates being capable of axial movement and being penetrated by the pump shaft 3 and the stop pin 13, thereby being held fixed against relative rotation.

The axial plate at the front in the direction of view is not shown because it would obstruct the view. In the illustrated and described embodiment of the invention, the axial plates 19 have the approximate shape of circular segments which are taller than their radius. A radius of the axial plates 19 is smaller than an outer radius of the annulus 4 and larger than a root circle radius of the annulus 4, with the result that the axial plates 19 cover interspaces between the teeth of the gearwheels 2, 4. In the circumferential direction, the axial plates 19 completely cover the filler piece 9 and the free space 6 between the gearwheels 2, 4 on the pressure side of the internal gear pump 1, and partially cover it on the suction side, ensuring that the pump inlet 7 remains free. On the outer sides thereof, which face away from the gearwheels 2, 4 and the filler piece 9, the axial disks 19 are subjected to the pressure of the pump outlet 8, i.e. to the pressure of the pressure side of the internal gear pump 1, and are thereby pressed into or held in sealing contact with the side faces of the gearwheels 2, 4 and the sides of the axial sealing element 14 in the filler piece 9. As already stated, the axial sealing element renders the axial plates 19 provided for axial compensation superfluous, even if the axial plates 19 are present in the illustrated and described embodiment of the invention. The axial sealing element 14 enables lateral sealing of the filler piece 9 without axial compensation on rigid inner end faces of the pump casing 5 facing the gearwheels 2, 4 and the filler piece 9 and/or axial compensation on the housing cover (not shown).

One of the two axial plates 19 has a punched tab which is bent inward, i.e. between the two gearwheels 2, 4, and forms an abutment 20 for the filler piece 9. The abutment 20 is situated on a pressure-side end of the outer part 10 and of the inner part 11 of the filler piece 9 and secures the filler piece 9 against movement in the direction of the pressure side. By means of a punched opening 21, out of which the abutment 21 is bent inward, the pressure region of the free space 6 communicates with the pump outlet 8. The tab forming the abutment 20 is formed by bending inward, i.e. by forming, on one axial plate 19. 

1. An internal gear pump, comprising: an internally toothed annulus; an externally toothed pinion arranged eccentrically in the annulus and configured to mesh with the annulus in one section of a circumference; a crescent-shaped free space between the pinion and the annulus opposite said one section of the circumference in which the pinion meshes with the annulus; and a filler piece arranged in the free space, and having an inner part and an outer part, wherein the inner part has an inner side on which tooth tips of teeth of the pinion rest, wherein the outer part has an outer side on which tooth tips of teeth of the annulus rest, and wherein an axial sealing element is arranged between the inner part and the outer part.
 2. The internal gear pump as claimed in claim 1, wherein one of the inner part and the outer part of the filler piece is a bent sheet metal part.
 3. The internal gear pump as claimed in claim 1, wherein the axial sealing element is configured to press the inner part of the filler piece elastically inward against the tooth tips of the teeth of the pinion and is configured to press the outer part of the filler piece elastically outward against the tooth tips of the teeth of the annulus.
 4. The internal gear pump as claimed in claim 1, wherein the axial sealing element has a cavity configured to communicate with a pressure side of the internal gear pump.
 5. The internal gear pump as claimed in claim 4, wherein: the axial sealing element is U-shaped and is closed at an end facing a suction side of the filler piece, and the axial sealing element includes a first leg along an inner side of the outer part of the filler piece and includes a second leg along an outer side of the inner part of the filler piece.
 6. The internal gear pump as claimed in claim 1, wherein the axial sealing element is connected to the inner part and to the outer part of the filler piece.
 7. The internal gear pump as claimed in claim 6, wherein the inner part and the outer part of the filler piece are shaping elements during production of the axial sealing element.
 8. The internal gear pump as claimed in claim 1, further comprising a pressure-side abutment for the filler piece.
 9. The internal gear pump as claimed in claim 8, further comprising an axial plate including the pressure-side abutment for the filler piece.
 10. The internal gear pump as claimed in claim 9, wherein the pressure-side abutment is made by forming.
 11. The internal gear pump as claimed in claim 1, wherein the gear pump is for a hydraulic vehicle brake system. 